Small waterplane area multihull (SWAMH) vessels are multihull vessels comprising at least two submerged hulls which are connected to a work platform or upper hull that resides above the water. Connections are made by elongated struts which have a cross-sectional profile substantially smaller than that of the submerged hulls. Constructed in this manner, the vessel through water presents a platform or hull which is relatively insensitive to water surface disturbances; however, large propulsive forces are required to impel a SWAMH vessel due to combined effects of frictional resistance of the large wetted surface of the hulls and interference resistance occurring as an interaction between the twin hulls. Numerous attempts have been made to improve the performance of watercraft in general and of SWAMH vessels in particular, whether to improve the buoyancy, durability or handling capabilities of a vessel or to improve the performance characteristics of passive motivating means such as sails or active motivating means such as engines or oars.
Attempts have been made in the prior art to improve both buoyancy and performance have included using multiple hulls and double walled hulls having a buoyant material entrained therebetween. For example, U.S. Pat. No. 3,811,141, issued May 21, 1974 to Stoeberl; U.S. Pat. No. 3,911,190, issued Oct. 7, 1975 to Myers et al.; U.S. Pat. No. 4,094,027, issued Jun. 13, 1978 to Vernon and U.S. Pat. No. 4,118,814, issued Oct. 10, 1978 to Holtom disclose double walled boat hulls, typically for multi-hull vessels, that include a buoyant material such as a gas or foam between the walls. U.S. Pat. No. 5,613,460, issued Mar. 25, 1997 to Stallard shows a submarine which has an outer skin which surrounds a foam. This foam is intended to provide buoyancy to compensate for external weapons launch systems.
U.S. Pat. No. 3,842,772, issued Oct. 22, 1974 to Lang teaches a vessel shaped to reduce the effect of large waves striking a platform. The semi-submerged ship has two elongated hulls which include a propeller at the stern thereof. U.S. Pat. No. 4,557,211, issued Dec. 10, 1985 to Schmidt, similarly has a pair of submerged hulls. The hulls provide a buoyancy support for the upper hull and have propellers at the sterns thereof. U.S. Pat. No. 5,313,906, issued Zapka discloses a SWAMH vessel per se. U.S. Pat. No. 5,184,561, issued Feb. 9, 1993 to Nickell, Jr. shows a vessel including finned planing pontoon hulls.
U.S. Pat. No. 3,338,203, issued Aug. 29, 1976 to Moore shows a watercraft hull fashioned of plural lighter than air gas filled compartments and U.S. Pat. No. 4,802,427, issued Feb. 7, 1989 to Biegel discloses a ship hull including sub-hulls that reduce pitch, roll and yaw. U.S. Pat. No. 5,178,085, issued Jan. 12, 1993 to Hsu teaches the wave cancellation properties of a multi-hull ship.
Propulsion systems have been the targets of improvements as in U.S. Pat. No. 4,838,819, issued Jun. 13, 1989 to Todorovic which discloses a marine propulsion unit including a ducted turbine having side inlets. U.S. Pat. No. 4,505,684, issued Mar. 19, 1985 to Holden et al. shows a thrust tube propulsion system including propellers disposed within the thrust tubes. U.S. Pat. No. 5,722,866, issued Mar. 3, 1998 to Brandt; U.S. Pat. No. 5,435,763, issued Jul. 25, 1995 to Pignata and U.S. Pat. No. 5,181,868, issued Jan. 26, 1993 to Gabriel relate to belt- and gear-driven turbines.
U.S. Pat. No. 2,941,495, issued Jun. 21, 1960 to Goldman shows a water craft propulsion system utilizing an impeller with spiral veins and a housing. U.S. Pat. No. 3,055,331, issued Sep. 25, 1962 to Singelmann teaches a centrifugal pump assembly driven with a turbine which is propelled by a jet engine. U.S. Pat. No. 5,722,864, issued Mar. 3, 1998 to Andiarena shows a marine propulsion system which includes a rotational unit having blades rigidly secured to the inner periphery of the rotational unit.
Despite the teachings of the prior art, a need still exists for a multihull vessel which is stable, maneuverable and sturdy and which can efficiently accommodate an active propulsive means which optimizes the passage of the vessel through the water.